Modern pipelines are used to efficiently transport various solid, gas and liquid materials. Exemplary materials include crude oil, gasoline and natural gas. Regardless of the type of materials they transport, the ability to perform various operations on a pipeline with minimal disruption to the flow of product is essential in the pipeline industry.
A pipeline inspection gauge or “pig” is a tool inserted into the flow of material through a pipeline and propelled by the pressure of the material being transported in the pipeline. Uses for pigs include, but are not limited to: 1) physical separation between different materials being transported in the same pipeline; 2) cleaning of the internal surfaces of a pipeline; and 3) inline-inspection of the integrity of the pipeline.
It is generally believed that pigs where first used in the United States in the mid to late 1800's as the oil industry replaced horse drawn transportation with pipelines for the transportation of crude oil from well sites to refineries. The oil industry discovered that over time internal deposits in the pipelines restricted the flow of materials resulting in higher pumping pressures and decreased efficiency. To improve flow, the companies began bundling various materials together to insert into the pressurized stream of material. As these bundles of material passed through the pipeline they would dislodge deposits and provide immediate flow improvement. It is rumored that early pigs were made of bundles of leather or straw wrapped in wire. As these bundles traveled through the pipeline there were said to make a squealing noise sounding like a pig. The term “pipeline inspection gauge” is thought to have been created later as a backronym.
There are several different types of modem day pigs. There are “batching” or “swabbing” pigs that are designed to act as a simple barrier between dissimilar fluids or to provide a sweep of a pipeline. If more than a simple sweep is desired, more elaborate “cleaning” pigs can be used. Cleaning pigs can be mounted with all manner of brushes, scrapers, blades or aggressive high tensile strength steel protrusions for removing interior deposits or scales. Pigs specially designed for inline inspection rather than cleaning include “gauging” pigs which include a simple gauge plate made of soft material which deforms when it collides with a protrusion on the interior surface of the pipeline or “smart or intelligent” pigs which carry out complex tasks such as logging data for mapping, geometric measurement, crack detection, measurement of metal loss, and many other tasks as they travel through a pipeline.
As explained above, most pigs are propelled by the pressure of the material being transported in the pipeline. They accomplish this propulsion through the simple creation of a pressure differential between the rear and front sides of the pig. Most pigs achieve this differential pressure gradient though the use of one or more sealing elements which positively engages the interior surface of the pipeline thereby creating a frictional force working opposite to the desired direction of travel. The pressure applied to the rear side of the pig by the pressurized material increases to overcome the opposite frictional force created by the sealing element(s) thus creating the pressure differential between the rear and front side of the pig. Eventually, pressure on the high side exceeds the frictional force, and the pig moves in the direction of the low-pressure front side thereby propelling the pig in the direction that the material is flowing in the pipeline.
As also explained above, it is important to be able to perform the cleaning, batching and inspecting functions on pipelines for which pigs are designed, without shutting down or otherwise interrupting the flow of materials. To minimize any interruption as much as possible, pipelines are often equipped with secondary pipeline chambers from which pigs can be inserted or removed from the main pipeline. These chambers, referred to commonly as “pig launchers” and “pig catchers,” are connected to the main pipeline via a series of valves. These valves allow for the opening and closing of the chamber to the main pipeline and for the routing of pressurized material from the main pipeline to the rear of the chamber to pressurize the chamber once the pig is loaded and ready to be injected into the main line.
The increased size of the pipelines, combined with increased pig complexity, has led to an increase in size and weight of modem pigs. As explained in U.S. Pat. No. 6,925,671, the industry has in the past relied upon man power, sometimes in combination with trucks or other non-specialized vehicles, to insert and extract pigs. Due to safety considerations, for example ignition of flammable materials being transported in the pipeline or crushing injuries caused by the loss of control of the pig, a need exists for a portable device which can be easily and quickly positioned in front of the pipeline and used to quickly extract a pig with a minimal use of man power and minimal reliance on other devices such as trucks, tractors, backhoes, etc.